There are a number of situations in hydrocarbon wells where it is necessary or desirable to position a tool at a predetermined location in the well. In vertical wells, tools are conventionally run on the bottom of a wire line and use gravity to cause the tool to fall into the well. In horizontal wells, gravity can be used in the vertical leg but only for a very short distance into the horizontal leg. It has become customary to pump the tool on the end of a wire line to its desired location in the horizontal leg of a well. Pumping a liquid into the pipe string creates a dynamic pressure differential across the tool thereby propelling it along the horizontal leg. Because the tool is on the end of a wire line, the distance the tool is pumped can be controlled.
One problem with this approach is that substantial quantities of the pumped liquid, which is usually raw or treated water, are needed because creating a dynamic pressure drop across the tool requires that a large volume of liquid be pumped across the tool. It is not surprising to require twenty barrels of water a minute to propel a tool at an appropriate velocity in the horizontal leg of a hydrocarbon well. The volume required to pump the tool to its desired location is a simple multiplication of the pump rate and the pump time. It is not unusual to consume many hundreds of barrels of water to propel a tool a substantial distance in the horizontal leg of a hydrocarbon well.
A conventional approach is to provide a more-or-less rigid pump down collar on the exterior of pump down tools as shown in U.S. Printed Patent Applications 20100263876; 20110277989; 20120118561 and 20120145379 to reduce the gap between the outside of the tool and the inside of the pipe string.
Other disclosures of some interest relative to this invention are found in U.S. Pat. Nos. 2,644,523; 3,346,045; 3,347,196; 4,356,865; 4,392,528; 4,423,783; 4,828,291; 4,961,465; 5,095,980; 5,180,009; 5,209,304; 5,927,402; 6,138,764; 6,460,616; 6,467,541; 6,739,391; 6,973,971; 7,025,142; 7,182,135; 7,261,153; 7,322,421; 7,434,627; 7,686,092 7,753,130 and 8,079,413 and U.S. Printed Patent Application 20050241824.